The present invention, in some embodiments thereof, relates to hair removal and, more particularly, but not exclusively, to hair removal by ultrasound.
A hair is composed of a protein named keratin arranged in three layers, termed the outer cuticle, the middle cortex and the central medulla. Hair grows from a follicle, which is a small cup-shaped pit buried under the skin. The walls of the follicle form the outer root sheath of the hair. The base of the hair follicle, called the dermal papilla, is fed by the bloodstream which carries nourishment (e.g., nutrients and oxygen) to produce new hair and removes waste materials formed in the process (e.g., CO2). The lower part of the follicle widens out to form a hair bulb containing a germinal matrix, which is the source of hair growth. Hair growth is initiated in the hair bulge, which is a small swell of the hair follicle that forms the attachment site of a small smooth muscle, called the arrector pili muscle. During the anagen phase (the growing phase of the hair), the dermal papilla sends signals to the stem cells in the hair bulge to migrate downwards along the follicle. Triggered by the dermal papilla, the stem cells begin to proliferate and, following cell differentiation, a new hair shaft is formed.
Various methods and devices exist for removal of undesired hair. Known devices generally pluck hair affixed to a tissue using various types of gripping, pulling and/or cutting means. The existing techniques can be classified into two major categories: short-term and long-term hair removal techniques.
In short-term hair removal techniques, the hair is removed without significantly damaging the biological regeneration and/or re-growth mechanisms found at the base of each hair. Such technique affects only that part of the hair shaft, which is located outside the skin, while the living part of the hair (in the hair follicle attached to dermal papilla) continues to grow. The most common short-term hair removal techniques include: shaving, rotary mechanical epilation, waxing and chemical depilation.
Long-term hair removal techniques affect the biological re-growth mechanisms of the removed hair, and thus have the potential of inhibiting re-growth of unwanted hair from the treated organ. The most common long-term hair removal techniques include: electrolysis, laser and intense pulsed (non-laser) light.
Electrolysis is performed by transmitting a direct current to the hair root in order to form hydroxyl ions that electrochemically destroy the germinative cells of the hair follicles. Electrolysis can also be performed using high frequency currents to heat the water of the hair follicle and to coagulate the germinative hair cells.
U.S. Pat. Nos. 5,632,741 and 5,752,948 disclose methods for hair removal by laser radiation. The hair follicle is irradiated by focused laser beam, resulting in a temperature rise and a destruction of the follicle.
In the intense pulsed light method, filtered light energy is converted in the dermis to heat and absorbed by hair pigment to destroy the hair structures and impair hair re-growth. This method has a much larger spot size than traditional laser technology, hence can cover the treatment area faster and in fewer sessions. On the other hand, in this method, larger areas of the skin are in danger of developing side effects such as thermal injury and pigmentation changes. Some extent of relief to the skin can be provided by extending the duration between successive pulses of light.
U.S. Pat. No. 4,566,454 discloses the application of radiofrequency waves to the hair at a frequency selected such that the hair impedance to radiofrequency energy conduction is substantially lower than at other radiofrequency frequencies. Generally speaking, the main principles of this technique consist of finding and selecting a radiofrequency resonant frequency for a given hair to reduce its impedance, since the resonant frequency varies from hair to hair. Another technique, disclosed in U.S. Pat. No. 5,470,332, consists of a pre-treatment of the hair prior to applying electromagnetic energy thereto. This pre-treatment makes the hair more receptive to the electromagnetic energy prior to its reaching the root of the hair.
International Patent Application Nos. WO 01/13757 and WO 01/033991 disclose hair removal methods in which a hair to be removed is subjected to low frequency vibrations. The low frequency vibrations are transmitted to the hair root either through the hair (WO 01/13757) or by irradiating a treatment zone (WO 01/033991) and exert a force to cause the root to disconnect from the surrounding tissue. The disconnection is mainly due to relatively large vibration amplitude (tens of micrometers to a few millimeters, depending on the vibration generator) of the hair shaft. WO 01/13757 and WO 01/033991 recite a frequency range of four orders of magnitude (10 Hz to 100 kHz), but teach that the preferred vibration frequency is in the sub kilohertz range.
International Patent Publication No. WO 01/26735 discloses a technique for the removal of undesired hair by utilizing ultrasonic resonating waves at a treatment zone in a close proximity to the hair to be removed.
International Patent Publication No. WO 00/21612 discloses a technique for the removal of undesired hair by utilizing ultrasonic forces. The technique involves the production of a focused ultrasonic beam having an acoustic focal point in which the area of the beam is smallest and the intensity of the beam is the highest. The ultrasonic beam is irradiated through the skin, it penetrates through the skin layers above the hair papillae and its focal point reaches the papillae. The parameters of the beam are such that the intensity per unit area on the skin is sufficiently small not to damage the skin above the papillae, while at the focal point the ultrasonic energy is said to be high enough in order to destroy living cells. WO 00/21612 recites a three orders of magnitude range of ultrasound frequencies (20 kHz to 25 MHz), but teaches that the preferred ultrasound frequency is in the range of 3000 kHz to 7000 kHz. WO 00/21612 also teaches generation of cavitations within the hair root, by irradiating using ultrasound waves at a frequency range of 1 kHz to 5 MHz.
International Patent Publication No. WO 02/09813 discloses a hair removal method in which the area from which the hair is to be removed is struck by ultrasonic waves until the temperature of the tissues is raised-as a result of the absorption of the energy carried by the ultrasonic wave-to a degree sufficient to cause damage to the hair follicle. Similarly to WO/0021612 as described hereinabove, WO 02/09813 teaches that the ultrasound waves should be focused, so as to obtain a focal spot with lateral dimensions of order of a few tenths of the millimeter and a longitudinal extension of a few millimeters. The small focal spot has to be precisely directed onto the follicle to cause the desired destruction.
International Patent Publication No. WO 03/065347 discloses a method of treatment of tissue by a focused beam of ultrasonic vibration. WO 03/065347 employs a plano-concave lens which focuses the ultrasonic vibration at the treatment zone.
U.S. Patent Application, Publication No. 2002/0165529 discloses a method of treating subcutaneous tissue to achieve a therapeutic effect of hair removal. The therapeutic effect can be achieved by delivery of ultrasound energy to subsurface tissue. Two or more ultrasound delivery elements are positioned in an array in a manner such that their resulting output constructively interferes and focused onto the desired subsurface location.
International Patent Publication No. WO 99/029245 discloses a method of permanents hair removal method that includes two treating steps. In a first step, ultrasound is used to introduce alkaline ions into the skin and around the hair follicles, and a second step potentiates the destructive chemical reaction between the alkaline ions and the hair follicles, using radiant energy in the visible region.
U.S. Pat. No. 6,544,259 discloses a hair removal method in which radio frequency radiation is applied to a selected skin zone so as to destroy the hair follicles. Subsequently, ultrasound waves are applied to the skin zone to shake up the hair with the destroyed follicle and thus slacken the union between the hair and the skin zone and underlying area. Once the union is slackened the hair is pulled out of the follicle.
U.S. Pat. No. 6,200,326 discloses a method and apparatus for long-term removal of hair by transmitting ultrasound energy to a needle passed through the skin into an individual hair follicle. The resulting cavitations within the area surrounding the hair follicle causes the hair follicle to be disrupted.
International Patent Publication No. WO 2005/079687 discloses a technique in which acoustic waves are transmitted through the hair so as to generate heat at a follicle, a dermal papilla, a hair bulge and/or a germinal matrix of the hair. The heat is in itself sufficient to damage and/or destroy the follicle, the dermal papilla, the hair bulge and/or the germinal matrix.
Additional background art includes Japanese Patent Nos. JP 2001029126 and JP 8154728.